Not Applicable.
Not Applicable.
This invention relates to the field of payload fairings for launch vehicles and more particularly, to an improved payload fairing utilizing a jettisonable mass to provide improved acoustic suppression characteristics.
It is known that launch vehicles of payloads such as satellites require measures to protect the payload from the sound fields generated by lift-off and flight. It is also known that as new higher energy launch vehicles are utilized the increased total lift-off thrust of these vehicles produces higher acoustic field intensities than current launchers. Therefore, conventional measures for protection of payload are inadequate.
A fairing is the shroud or cover that surrounds the payload or cargo which will be launched for use. Generally, the cargo is a satellite although any other instrument or vehicle may be launched. The fairing protects the payload from the atmosphere. When the launch vehicle is above atmosphere the fairing is jettisoned. The payload is released when the propulsion operations are completed. Currently, fairings are generally constructed with a solid metal wall or a layered wall including a standard hexagonal cell aluminum honeycomb core with composite face sheets. These xe2x80x9cbare wallxe2x80x9d fairings do not adequately protect some payloads from damage. The robustness of the payload varies. Some payloads are more fragile and sensitive than others. These payloads require more protection.
The payload must be protected from the high temperatures, large forces, and vibrations due to noise encountered during launch. The acoustic energy produced can damage the payload. The acoustic energy can reach 150 dB which produces vibrations that can lead to mechanical damage. In the case of satellites, antennas or other appendages can break. Circuit boards can be damaged and mirrors or lenses can be damaged or moved out of alignment. Any resulting damage can seriously degrade or totally impair the capabilities of space launched equipment.
Acoustic blankets have been used to absorb the acoustic energy to protect the payload. The blankets are attached to the inside surface of the fairing wall. These blankets are usually made of fiberglass batting or a combination of fiberglass sheets and batting which are of different thicknesses and are layered together. The use of blankets has been found to be most effective at frequencies above 300 Hz but does not provide enough protection below about 100 Hz. For frequencies of greater than 300 Hz, the wavelengths are fairly short and the acoustic energy can be fairly easily absorbed by the blankets. However, for frequencies below 100 Hz, the wavelengths are fairly long and there is not a sufficient depth of material in blankets to absorb a significant portion of the energy. Therefore, the blankets are not very effective at these frequencies. In the past, to increase effectiveness of the blankets the thickness has been increased to provide more absorption. As the thickness of the blankets is increased, the cost, volume, and weight of the blanket is increased. Of course, an increase in weight and volume of the blanket decreases the weight and volume available for payload. Thus, the launch vehicle payload lift capability is adversely affected by use of thick, heavy blankets.
Two other approaches to reducing acoustic transmission through the fairing wall have been taken. The stiffness of the wall has been increased and the mass per unit area of the wall has been increased. Neither of these approaches are considered desirable because they usually increase fairing weight, which reduces payload weight delivered to orbit.
Consequently, a need remains for a payload fairing which can suppress the acoustic energy generated by the launch of the payload to protect the payload without penalizing vehicle lift capability. The invention provides high acoustic attenuation over a wide frequency band including low frequencies.
The invention is a payload fairing including a number of layers of material that surround the payload and also act as an acoustic damper to protect the payload from excess acoustic energy generated during lift off and launch.
The payload fairing or shroud comprises a wall for forming the fairing structure including face sheets typically fiber-resin, bonded to each side of a porous layer or core, typically two-dimensional aluminum honeycomb. The fiber-resin face sheets form an inner and outer skin. A water barrier is included as part of the inner skin. The honeycomb material is a two-dimensional honeycomb and is generally aluminum. Each of the inner and outer skins comprises carbon-epoxy face cloth or weave and carbon-epoxy tape or load skin. The inner and outer skins are the structural layers which provide strength to the fairing wall. The modified honeycomb layer is filled with a liquid which is held in place by the inner and outer skins. The shroud includes drain ports which are opened at a predetermined time during vehicle launch and the liquid is drained out of the shroud.
One advantage of the invention is that it provides high acoustic attenuation over a wide frequency band. As stated above, for frequencies above 300 Hz the wavelengths are fairly short and are more easily absorbed and for frequencies below 300 Hz the wavelengths are longer and the usual depth of blanketing material does not provide adequate protection. However, with the present invention the construction and materials of the fairing provide improved damping capabilities even at frequencies below 300 Hz. The liquid mass and the damping provided by the two dimensional honeycomb core in the fairing wall allows for better dissipation of the acoustic energy.
Another advantage of the invention is that there is little impact on the payload lifting capability of the launch vehicle. The mass added by the liquid suppression layer is jettisoned as early as possible in flight. The rapid draining of the liquid decreases the total vehicle weight early in the flight. Therefore, the invention utilizes the liquid suppression layer when noise levels are at the highest to provide the added damping protection needed for today""s launch requirements but the liquid is not carried through the entire launch so that vehicle lifting capability is not significantly affected.
Yet another advantage of the invention is that the cost and manufacture of the inventive fairing is reasonable. The invention provides a reasonably priced practical approach to protecting payloads from high acoustic levels.
These and other advantages and features which characterize the invention are pointed out with particularity in the claims annexed hereto and which form a further part hereof. However, for a better understanding of the invention, its advantages and objects obtained by its use, reference should be made to the drawings which form a further part hereof, and the accompanying detailed description in which there is shown and described an illustrative embodiment of the invention.